Microstructure and Mechanical Properties of Mg-6Zn-0.6Zr-0.4Ag-0.2Ca-xLi Alloys (x=6, 8 and 11 wt.%)

摘要

Recently, researchers have again highlighted a sheet-forming process of Mg alloys, due to increasing demand for Mg wrought alloys in the applications of casings of mobile electronics and outer-skins of light-weight transportation. Microstructure control appears essential for the enhancement of the workability and formability of Mg alloy sheets. Adding lithium to magnesium alloys can transform the hcp to bcc, substantially increasing the ductility of the Mg-Li alloys, while further reducing its density. Mg-Li alloys exhibit two phase structures between 6 and 11 wt.% Li contents, consisting of alpha-Mg (hcp) and beta-Li (bcc) phases. The beta single phase structure exists for greater than 11 wt.% Li contents. We investigated the effects of Li addition on the microstructure and mechanical properties of the as-cast and as-extruded Mg-6% Zn-0.6% Zr-0.4% Ag-0.2% Ca-based alloys. We cast the Mg-6Zn-0.6Zr-0.4Ag-0.2Ca-xLi alloy under an SF6 and CO2 atmosphere at 720 degrees C, extruded at 200 degrees C. Li addition to Mg-6Zn-0.6Zr-0.4Ag-0.2Ca-based alloy resulted in the formation of a Mg2Zn3Li intermetallic compound with random basal texture. The ultimate tensile strength slightly decreased from 238 to 236 to 198 MPa, with increasing Li addition from 6 to 8 to 11 wt.% Li, respectively. However, the elongation of the alloys remarkably increased from 15.7 to 37.8 to 55.4% by the same addition of the Li element. We clearly consider that the random texture and bcc beta-Li phase by Li addition contributed to the increase in the elongation and formability.